1. Field of the Invention
The present invention relates to a linear drive ultrasonic motor.
2. Description of the Related Art
A vibration apparatus in Japanese Patent No. 3524248 Specification (FIG. 9 and FIG. 10) can be cited as an example of a conventional linear drive ultrasonic motor. Here, FIG. 9 and FIG. 10 are diagrams showing a structure of the conventional linear drive ultrasonic motor, where, FIG. 9 is an exploded perspective view, and FIG. 10 is a vertical cross-sectional view.
The vibration apparatus shown in FIG. 9 and FIG. 10 includes a case 906 which accommodates a vibrating body 901, a mobile object 904 which passes through the case 906 and makes a contact with the vibrating body 901, and a pressing spring 905 which generates thrust (a bias) which brings the mobile object 904 and the vibrating body 901 in a pressurized contact. The pressing spring 905 is installed at an outer side of the case 906. An opening portion is formed in a side of the case 906, facing the vibrating body 901, and the thrust of the pressing spring 905 acts on the vibrating body 901 through the opening portion. In other words, this vibration apparatus has a structure in which, the pressing spring 905 is installed on the outer side of the case 906 while covering the opening portion of the case 906, and a deformed portion (a flat surface portion covering the opening portion) of the pressing spring 905 which generates the thrust, is exposed.
As in the vibration apparatus described in Japanese Patent No. 3524248 Specification, structuring main components in a packaged unit is effective from a point of general versatility and stabilization of characteristics. Whereas, in an ultrasonic motor apparatus, a small size and a high output have been sought.
In the vibration apparatus described in Japanese Patent No. 3524248 Specification, the structure is such that the mobile object 904 is guided in a direction of movement and around an axis of the mobile object 904 by a sliding bearing which is provided in a hole of the case 906. In this structure, since the mobile object 904 is pressed against the case 906 by the pressing spring 905, a contact pressure of a contact portion with the sliding bearing provided in the hole of the case 906 is high, and a sliding friction when the mobile object 904 moves is substantial. Therefore, a sliding resistance becomes substantial and causes degradation of the output. Moreover, since the mobile object 904 is vibrated by the vibrating body 901, a wearing out of a sliding-friction portion is accelerated. For instance, when a bearing such as a thrust bearing which is used generally in this portion is used, it leads to an increase in the apparatus size. Moreover, in the vibration apparatus described in Japanese Patent No. 3524248 Specification, providing a guide mechanism which guides the mobile object 904, at an interior of the case 906 is difficult from a point of view of small sizing, and furthermore, it is difficult to forma guide mechanism having a less frictional resistance while maintaining the small size, at the interior of the case 906.